If everything lines up now it theoretically should later. But having the frame checked would not hurt, depending on the $$ involved.
If you decide on having the frame checked then I would call the frame shop that you plan on using and ask them which way they would prefer, bare frame or whole truck.
If it were me and they could not do it as a bare frame, I would find another place to have it done.
This was posted on here before and would / could help,
http://www.chuckschevytruckpages.com/framespecs.html
With this you might be able to do this yourself.